This invention relates to a non-flared fitting for connecting, in fluid sealing relationship, a tubing end to another fluid conducting member, such as a piece of laboratory equipment or another tubing end.
The invention has particular adapation for use in liquid chromatography, providing a low to medium pressure connection, i.e. below about 1,000 p.s.i., between various types of tubing and such laboratory equipment such as chromatography equipment chemical metering devices, amino acid sequencers, or DNA sequencers.
Prior to applicant's invention, most low to medium pressure liquid chromatography and chemical metering systems utilized a fitting in which plastic tubing was flared to form a leak-free seal. To form the connection, the tubing had to be heated and formed using a special flaring tool. Such a procedure was not only bothersome and time consuming, but connections were only possible with tubing made of a thermoplastic material such as Teflon (tetrafluoroethylene) or other heat deformable material. Connections to rigid materials such as glass or metal, or other non-heat deformable plastics required special adapters.
Such connections were not conducive to quick changes and repairs in the laboratory.
The present invention totally eliminates flaring of the tubing as a basis for a seal between the tubing and the fluid conducting member. Thus the problem of connection to rigid tubing is eliminated and the need for flaring procedures and tools or adapters is unnecessary. No modification to the tubing is required. The connection is made by simply sliding a nut and ferrule onto the tubing and tightening into place. The connection thus can be made quickly and easily regardless of the type of tubing being connected.
In accordance with this invention, a fitting is provided for connecting in fluid sealing relationship a tubing end to a fluid conducting member having a fluid port, an end wall surrounding the port and a threaded portion extending from adjacent the end wall. The fitting comprises a ferrule of resiliant deformable material having a forward portion which is substantially wider than the tubing diameter and the end surface of which is configured to mate with and sealingly engage the end walls surrounding the port. The ferrule also has a rearward portion adapted to surround the tubing end. An axial throughbore extends through the ferrule with its diameter through the rearward portion being sufficient to receive the tubing end and its diameter through the forward portion being smaller than the tubing exterior, thereby forming a tube-abutting shoulder at the juncture of the forward and rearward ferrule portions. This is an important aspect of the invention and results in the tubing end being totally contained within the ferrule and being prevented from contact with the fluid conducting member. The second portion of the fitting comprises a fastener which has an axial throughbore for receiving the tubing. The fastener throughbore is flared at the forward end to present a conical fastener wall for axially engaging the rearward end of the ferrule. The fastener has a threaded portion for threadedly engaging the threaded portion of the fluid conducting member so that when the threaded portion is tightened on the threaded portion of the fluid conducting member, the conical forward wall of the fastener will engage and force the rearward end portion of the ferrule inwardly into sealing engagement with the surrounded tubing end and it will also force the forward end portion of the ferrule axially forwardly into flat sealing engagement with the end wall surrounding the port of the fluid conducting member.
Thus, with the present invention, there are two seals provided. The first of these seals is between the ferrule and the tubing at approximately the entry point of the tubing into the ferrule, i.e. at the rearward end of the ferrule. The second seal is between the preferably enlarged flat forward surface of the ferrule with the end walls surrounding the port of the fluid conducting member.
It is preferred that the ferrule have an inwardly tapered rearward end portion for engagement with the outwardly tapered conical throughbore walls of the fasteneing member. It is also preferred that the conical wall taper angle, as measured from the longitudinal axis of the fastener be be substantially greater than the taper angle of the rearward portion of the ferrule. This will cause the inward sealing force exerted by the conical walls at the forward end of the fastener to be concentrated at the extreme rearward end of the ferrule so that the fluid tight seal between the ferrule and the tubing will be at approximately the point the tubing enters the ferrule rearward portion.